Recently, the wireless communication technology has developed rapidly along with the advance of communication system technology, and the LTE system is one of the prominent 4th Generation mobile communication systems.
The LTE system adopts various advanced functions. For example, the LTE system supports heterogeneous network (hereinafter, referred to as HetNet) capable of accommodating the situation where the macro eNBs having relatively large coverage for dynamic eNB/cell deployment adoptive to various situation and supporting CSG cells for providing service to the restricted users.
In order to support the HetNet structure, the current standard is designed to select a pico cell with priority, even when the signal quality of the pico cell is bad, by ignoring the difference as much as the offset/bias applied to the pico cell in cell reselection. However, although the pico cell is selected with the offset/bias, if the pico cell of which signal is too bad to perform communication is selected, this causes problem. That is, the pico cell which selected with the advantage of the offset/bias value but of which signal strength is too bad to perform communication causes problem.
In the situation where the CSG cell and other cells coexist in the network, if the UE is not a member of the CSG cell, it may detects the signal of the CSG cell which is storing enough but cannot connects the corresponding cell.
FIG. 1 is diagram illustrating a heterogeneous network structure. In FIG. 1, the UE 305 cannot communicate with the CSG cell 303 although it is close to the CSG cell 303 physically. In this case, the UE 305 has to attempt connection to the macro eNB 301 but it is difficult to communicate with the macro eNB 301 due to the strong interference signal from the CSG cell 303.